1. Field of the Invention
This invention pertains to processing insulated electrical conductors, and more particularly to small wire stripping machines.
2. Description of the Prior Art
The process of cutting and stripping insulated electrical conductors in automatic machinery involves the use of pairs of cooperating blades, such as are disclosed in U.S. Pat. No. 4,577,405. The cutoff and stripping blades are typically clamped within two independent tool holders, with one blade of each pair being clamped in a different tool holder. The tool holders in turn are locked in place on separate opposed slides of a cutterhead mechanism. The cutterhead slides reciprocate toward and away from each other to close and open the blades. Closing the stripping blades forms a nearly perfectly round cutting hole circumferentially over the insulated electrical conductor to slice the insulation. The cutterhead is also translatable parallel to the electrical conductor axis to strip the sliced slug of insulation from the conductor. It is imperative that the closed stripping blades form a hole that closely conforms to the periphery of the conductor being stripped. Any skewness of the blades can result in scraped, nicked, or cut conductor strands.
Insulation cutting and stripping force requirements are very different for different size electrical conductors. A machine designed to process relatively large electrical conductors, such as 10 gauge wires, is overdesigned for use on smaller wires, such as 22 gauge wires. Conversely, the life of a machine designed for processing small wires but used for large wires is greatly shortened. Prior cutterheads include numerous levers, toggles, and other types of linkages to produce the necessary cutting and stripping forces. Such mechanisms are generally unsatisfactory for several reasons. They are frequently underdesigned and are prone to excessive deflections when used with heavy wire sizes. The various pivot points quickly wear and become sloppy. In many designs, linkage travel adjustments affect the force transmitted. For example, in one prior machine, an air cylinder rod operates a toggle linkage to open and close the cutterhead. The maximum extension of the cylinder rod determines where the toggle links stop. Accordingly, the force transmitted by the toggle links is a function of the allowed extension of the cylinder rod. Further with toggle mechanisms, if the links are closed past center when closing the cutterhead, the blades will actually open.
Other design flaws of prior cutterheads for processing insulated electrical conductors involve the fact that the two tool holders on the cutterhead are entirely independent of each other. The large number of components, such as slides and linkages, make an undesirable stack-up of tolerances unavoidable. Hence, proper alignment between the two independent tool holders is very difficult to achieve. Closely related is the fact that many prior machines utilize cast pieces to hold the cutting and stripping blades. Unfortunately, the casting process does not achieve the close tolerances required to accurately align and hold the blades.
The accuracy problem is greatly aggravated by the recent trends in the automotive and electronics industries to use ever smaller gauge conductors and thinner wall insulations. A typical small gauge/thin wall insulated electrical conductor has a conductor diameter of 0.029 inches and an insulation wall thickness of 0.011 inches. With an insulation wall thickness of 0.011 inches, the blades for stripping the insulation from the conductor must be capable of being adjusted to within approximately 0.001 inches. Because 0.001 inches is such a fine resolution, an accurate and rigid mechanical system for clamping and positioning the blades when forming the cutting hole is crucial.
Because of the accuracy problem inherent with prior insulated wire processing machines, operators traditionally insert the stripping blades into the machine without actually knowing the size of the cutting hole that will be formed by the closed blades. The operator then strips some test wires. If the blades cut the conductor, he adjusts the blades for a larger cutting hole size; if the blades do not completely cut through the insulation, he adjusts the blades for a smaller cutting hole size. In other words, present practice is to set stripping blades in a trial-by-error fashion.
Since different wire sizes generally require different blades and also different strip lengths, frequent changes to the tool holder set-ups are necessary. However, in prior cutterheads, it is difficult and cumbersome to remove and insert both the blades and the spacers that fill the tool holder cavities between the blades. Detailed information on tool holder spacers may be found in U.S. Pat. No. 4,784,024.
In many prior wire processing machines, the wire is vertically oriented with a vertical cutterhead. The blades reciprocate along a vertical axis. Scrap removal is a problem in those machines because the scrap insulation slugs tend to fall by gravity onto the lower blades. If that happens, the slugs can become trapped on the lower blades and prevent a good strip of the subsequent wire ends to be processed.
Thus, although numerous types of equipment are available for automatically cutting and stripping insulation from insulated electrical conductors, the existing equipment is not capable of meeting modern production requirements.